Roll finishing of metal strips or bars is a wellknown processing technique allowing for the continuous mechanical working of the metal until the desired physical dimensions are achieved. Such roll finishing is generally performed when the work metal is at a substantially elevated temperature, i.e., hot rolling, as this permits the most effective method of breaking down the as-cast structure of the ingot, with rolling forces generally tending to be lesser, and cast defects being more easily eliminated. In the case of hot rolling steel, the temperature of the steel may be approximately 1800.degree. F. (982.degree. C.) during the rolling process.
As the work metal passes through the rolls of the mill, a reduction in the thickness of the metal results in a corresponding increase in the length thereof inasmuch as the working volume remains constant. Furthermore, as it is appreciated in the rolling mill industry, the work piece cannot be introduced into the rolls of the finishing stand until after it has completely exited the rolls of the roughing stand. As such, depending upon the physical size of the rough-rolled work piece, a large area is required to accommodate the work piece during this transition period. In addition, because the work piece is at a substantially elevated temperature relative to the ambient temperature, cooling of the work piece will occur, thus affecting the hot rolling process. Particularly, as the work piece cools, scale may form on the exposed surfaces which, during the finishing operation, may result in unacceptable defects or blemishes in the finished strip.
Several methods have been utilized in the past to remedy this problem. One requires the removal of the scale prior to the initiation of the finishing stage. The scale is usually loosened and removed by jets of high pressure water. While this process may adequately remove the scale, it does not correct the underlying problem, namely, the cooling of the strip which results in increased rolling forces needed to complete the rolling process.
The more desirable solution to the scaling and cooling problem is to attempt to maintain the work metal at a constant, uniform temperature. One method is to coil the work strip as it exits the roughing stand. This process allows for a substantially reduced area needed to contain the work strip. Also, because of the juxtaposition of successive coils, less cooling occurs as a result of the reduction of surface area exposed to the ambient temperature. Nevertheless, the coil is not maintained at a constant temperature throughout, resulting in a non-uniform temperature of the strip and thus non-uniform finishing of the work strip.
Another method employed to alleviate the cooling and scaling problem is to apply heat to the entire length of an unfurled strip during the transition from the roughing stand to the finishing stand. This process necessitates a substantial amount of floor space to accommodate the work strip, thus resulting in ungainly, and expensive, rolling mill lines, and buildings in which to house them. Furthermore, an exorbitant amount of heat is required to provide uniform heating of the work strip. This results in an undesirable heating of conveyor rolls and their bearings and additionally is inefficient, and thus expensive, resulting in a vast consumption of fuel to maintain a uniform temperature in the work strip.
Despite the various attempts to maintain a uniform temperature of the work strip during the transition period between the roughing stand and finishing stand, none offers a relatively compact and energy efficient system which can maintain a constant, uniform temperature throughout the entire work piece in addition to providing for the removal of any scale which may form on the surface thereof.